In fields easily affected by the presence of a foreign material, such as the semiconductor field, there is a demand for a ring vacuum seal that does not release gas or particles. As a sealing ring, there have been conventionally known a rubber O ring (ring having an O sectional shape when cut to open the ring), a metal O ring, a C ring with a coil spring and the like. Of these, the rubber O ring is unsuitable for use as a vacuum sealing ring in this field, since it releases gas or particles. In contrast, the metal O ring serves as a vacuum seal, because it does not release a foreign material when washed thoroughly with water before use. However, this ring requires tight clamping for the exhibition of sufficient sealing function, which in turn gives rise to a need for a large clamping mechanism that can provide enough clamping force, consequently making the vacuum apparatus bulky.
As disclosed in Japanese Utility Model Unexamined Publication No. 92870/1989, for example, a C ring with a coil spring has a structure wherein a hard metal (e.g., stainless) helical coil is housed in a jacket having a C sectional shape. As this ring is made exclusively from metal materials, it, like a metal O ring, does not release a foreign material when washed thoroughly with water before use and the force necessary for clamping this ring is not as big as that for the metal O ring. Even this C ring with a coil spring, nevertheless, still requires a greater force than a rubber O ring to clamp the helical coil set inside. This in turn makes the clamping mechanism comparatively large, again making the vacuum apparatus bulky.
It is therefore an object of the present invention to provide a seal that does not release a foreign material into the sealed space and that does not require a great force for clamping.